The present invention is directed to a process and system for NOX removal at coal burning power plants, which includes introducing ammonia that is liberated upon drying a mixture of organic waste and coal combustion by-products having a pH of at least 9.5, to a coal burner in the power plant. The present invention is also directed to a process and system of fueling a coal burner of a power plant with coal and a dried mixture of organic waste and coal combustion by-products. The present invention is further directed to the dried mixture of organic waste and coal combustion by-products made by the processes of the present invention.
Mineral by-products have been used in stabilizing semi-solid, odorous organic waste through bulk drying, odor absorption, and granulation (see e.g., U.S. Pat. Nos. 3,877,920 and 4,554,002). In addition, mineral materials including sand, diatomaceous earth, perlite, and various mineral reagent powders have been used in conjunction with fluidized heating, drying and burning of sludges and oily waste (see e.g., U.S. Pat. Nos. 4,159,682, 4,787,323, 4,970,803, 5,490,907). However, existing thermal dryers have ongoing problems with drying waste high in organics, particularly sewage sludges, in the waste sticking to dryer surfaces, charring and producing burnt organic matter odors, and catching on fire.
Organic waste has traditionally been disposed of by incineration, primarily in stand-alone plants designed for a particular waste. Wet waste, such as dewatered sewage sludge filter cake, requires supplemental fuel to initiate and sustain burning, and sludges are not self-burning until solids contents are greater than about 30%. Dry organic waste such as paper and cardboard are net energy producers and municipal refuse incinerators that use these feedstocks are capable of significant power generation. Likewise, dried animal manures like broiler chicken litter, which contains sawdust that is used as bedding, can have a solids content in excess of 75% and can be incinerated with out supplemental fuel. Methods of more efficiently disposing of organic waste are desirable.
NOx created during the burning of coal can react with volatile organic compounds in the presence of heat and sunlight to form ozone. Gaseous ammonia, in the form of commercial anhydrous ammonia and its main derivative, urea, are currently used in treating fossil fuel combustion exhausts for NOx removal. This is a very expensive process, however. Therefore, inexpensive sources of ammonia or methods of recycling ammonia are desirable.
The present invention is directed to processes and systems for NOX removal at coal burning power plants, which include introducing ammonia liberated upon drying a mixture of organic waste and coal combustion by-products having a pH of at least about 9.5 or 10, to a coal burner in the power plant. The liberated ammonia that is introduced to the coal burner by the present processes and system, may supplement commercial anhydrous ammonia or urea added to the coal burner for NOx removal.
The present invention is also directed to processes and systems of fueling a coal burner of a power plant with coal and a dried mixture of organic waste and coal combustion by-products. The coal is preferably pulverized coal. In this embodiment, the dried mixture of organic waste and coal combustion by-products is a source of supplemental fuel to the coal burner.
The present invention is further directed to the dried mixture of organic waste and coal combustion by-products made by the processes of the present invention.
In the processes and systems of the present invention, the mixture of organic waste and coal combustion by-products optionally additionally contains lime. Additionally, during drying, the mixture is dried to preferably at least 90% solids. The drying preferably takes place in a direct or indirect dryer and preferably uses waste heat from the power plant.
Examples of organic waste used in the process of the present invention include, but are not limited to, dewatered sewage sludge filter cake, various animal manures, pulp and paper waste, shredded paper and cardboard, food waste, and other organic industrial waste.